1. Field of the Invention
The present invention pertains generally to the field of reclinable seats and more particularly is directed to a screw jack which is normally motor driven for adjusting the angular position of a recliner seat and which features a manual override to permit seat adjustment in the event of motor drive failure.
2. State of the Prior Art
It is conventional to provide recliner seats with a motor driven screw jack consisting of a long threaded screw coupled at one end to a motor mounted to the stationary seat bottom, the screw being threaded through a nut or equivalent female element connected to the reclineable back of the seat by means of a pivot arm. The nut moves axially along the screw as the screw is turned by the motor drive thereby pivoting the backrest in a direction determined by the direction of screw rotation.
The use of such power drive recliner mechanisms has been limited in certain applications which require the ability to adjust the backrest position even in the event of failure of the motor drive or failure of the power supply to the same. Manual override capability is indispensable, for example, in passenger aircraft seat installations subject to Federal Aviation Agency (FAA) regulations requiring that passenger seats be in a fully upright position during take-off and landing. Although it is desirable to provide electrically powered recliner seats in passenger aircraft, and attempts have been made to provide manually overrideable power drives for the same, the cost, complexity and other shortcomings of the available devices have severely limited the extent of their usage.
One known design for an overrideable recliner screw jack employs a lateral pin inserted through the housing of the device into the nut thereby normally fixing the nut to the housing, both nut and housing traveling along the screw upon power driven rotation of the latter. In case of power failure, the pin is withdrawn thereby freeing the housing from the nut and allowing manual repositioning of the seat backrest, the housing sliding axially over both the screw and nut absent any screw rotation. This known mechanism suffers from a serious shortcoming in that transmission of axial force between the device housing and the nut occurs through the single radial pin creating torque forces between the various components which create a susceptibility to mechanical binding, uneven or premature wear and otherwise unreliable operation. A particularly frequent problem with this design is the tendency for the locking pin to become wedged in place between the housing and the nut such that it becomes very difficult or impossible to extract it when it is necessary to do so.
Other power driven recliner screw jacks with manual override are available from European sources, and these are manufactured and assembled to very close tolerances in order to achieve the necessary reliability, but because of the high precision components used these devices are costly.
A continuing need therefore exists for a lower cost but reliable and efficient power driven recliner screw jack with manual override capability.